Axial piston unit usable as liquid pump and/or motor



United States Patent Inventor Appl. No. Filed Patented Assignee Priority AXIAL-PlSTON-UNIT USABLE AS LIQUID PUMP AND/0R MOTOR 3 Claims, 3 Drawing Figs.

U.S. Cl 91/505 Int.C| F041) l/02, F041) 9/00, FOlb 13/04 Field ol'Search 103/162; 230/l78;9l/198 1 z E 1" t E 1 E PRESSURE; L

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I I E b" 1--r-'----- --r-- E "1..- SUCTION E I [56] References Cited UNITED STATES PATENTS 3,075,472 1/1963 Garnier 103/162 3,092,034 6/1963 Bartholomaus 3,192,868 6/1965 Wahlmark 103/162 3,256,782 6/1966 Ebert 3,313,108 4/1967 Allgair et al.

Primary Examiner-William L. Freeh Attorney-Ernest G. Montague ABSTRACT: An uxial-piston-unit usable as liquid-pump and as -motor, respectively, which comprises an outer housing and a piston drum disposed in and rotatable relative to said housing. At least two ball or roller bearings guiding the piston drum and the latter has a plurality of cylinders arranged at equal distance from and parallel to the center axis of the piston drum. A piston is received and is sealingly guided in each of the cylinders. A drive shaft and holding shaft, respectively, are provided for the piston drum. An oblique disc is disposed in the housing operatively connected with the pistons such, that upon a relative rotation between the piston drum and the oblique disc, the pistons perform a reciprocating movement in the corresponding of the cylinders. The housing has control slots disposed on the opposite side of the piston drum for alsure-conduit. respectively.

PRESULTANT PRES as/rams MOMENT ON PISTON DRUM 15: M P E X e Patented Sept. 8, 1970 3,527,145

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AXlAL-PlSTON-UNIT USABLE AS LIQUID PUMP AND/OR MOTOR This is a continuation-in-part application of the copending patent application Ser. No. 588,782, filed Oct. 24, 1966, now abandoned.

The present invention relates to an axial-piston-unit useable as liquid-pump and/or motor.

Such liquid-pump and -motors are known already in most different embodiments. They comprise generally an outer housing, a piston drum having a plurality of cylinders with pistons sealingly guided therein, the pistons being disposed spaced equally from the center axis and parallel to the latter, the piston drum being rotatable relative to the housing, and they comprise further an input shaft and holding shaft, respectively, for the piston drum, which shafts project from the housing. They comprise still further an oblique disc disposed in the housing, the pistons being in operative connection with the disc such, that the pistons perform a reciprocating movement in the respective cylinders during a relative rotation between piston drum and oblique disc. They comprise also finally a control disc rigidly connected with the housing and disposed on the other side of the piston drum, whereby the end face of the control disc carries two kidney-shaped control slots for alternate connection of the cylinders with a suction conduit and pressure conduit by means of corresponding openings leading from the cylinders to the end face of the piston drum.

In practical operation of such axial-piston-pumps and -motors, it has been found, that a comparatively heavy wear occurred on the running face of the control member, in spite of careful selection of the best suitable working material for the control disc and the piston drum, which permit only corresponding limited operating periods of the units between the required overhauling by reworking of the control faces. The heavy wear of the control member was caused by the eccentric position of the resulting axial force onto the piston drum.

It is one object of the present invention to provide an axial piston-unit usable as liquid pump and/or motor, which avoids the heavy wear of the control faces, and, thereby, to increase the operating periods between the overhauling of the units, as well as the permissible working pressures.

It is another object of the present invention to provide an axial piston-unit useable as liquid pump and/or motor, wherein the control disc has at least one bearing pin rigidly secured to the control disc and disposed centrally and perpendicularly to the control face. The piston drum is guided in radial direction and strongly stiff against tipping, however, acljustably in axial direction on the bearing pin by means of two needle or roller bearings located at a distance from each other at or near the opposite ends of the bearing pin, so that the local surface pressure between the barrel and the control disc is reduced to a minimum, and is connected for joint rotation with the input and output shaft, respectively, however, within certain limits for angular and/or longitudinal movement, while the piston drum at its end face is maintained in engagement elastically with the control disc by means of a pretensioned spring. It has been brought about, by the simultaneous application of these features, to guide the cylinder drums in such stiff manner on the bearing pin rigidly connected with the control disc, so that the previously experienced one-sided running of the sealing faces, due to a certain yielding of the piston drum and of the bearing is practically completely removed and simultaneously the wear of the control faces could be reduced to a fraction of the previous values. The rotary connection, permitting within certain limits an angular and/or longitudinal movement, between the piston drum and its inputand output-shaft, respectively, prevents thereby with safety any tensioning of the piston drum guided solely by the double bearing on the pin of the control disc, whereby the use of at least one pretensioned spring for pressure engagement of the piston drum on the control disc permits the maintenance of an exactly defined face pressure in the control faces even in case of lacking working pressure, which face pressure assures a sufficient sealing with the least wear.

The structure of the axial-piston'units. designed in accordance with the present invention, is found most favorable in all different embodiments. A particularly important field of application is formed by such axial-piston-pumps and -motor, wherein an oblique disc is designed as swinging body adjustable to different oblique angles about an axis which is perpendicular to the longitudinal axis of the piston drum for variation of the feedingand suction volume, respectively. In such axial piston units an increased importance is assigned to a rotary mounting as stiff as possible against a tipping moment relative to the control disc, namely for the reason, because in a suitable arrangement of the tipping axis of the swinging bodies in or near the engagement plane between the piston-bottoms and the swinging body, the attacking point of the radial force effective over the piston drum mounting displaces itself in axial direction with the variation of the obliqueness of the angle, which arrangement is made for structural reasons, namely keeping small the outer diameter and of the adjustment forces.

Finally, it is within the scope of the present invention to apply the mounting of piston drums, as rigid as possible, in radial direction and against tipping, however, adjustable in axial direction, also to hydrostatic drives, wherein on both sides of the control disc a piston drum is provided, which is working as a pump and as a motor, respectively, the cylinders of the latter being in communication with channels connecting the kidneyshaped control slots of both control faces and extending through the control disc.

The bearing pins for the piston drums of the pumpand motor-part of such drives are suitably joined with a control axle rigidly connected with and passing through the control disc, the control axle being connected with the control disc, for example, by pressing in. The control axle is made of insethardened steel useable simultaneously as the inner track of the ball and roller bearings and is pressed into the control disc generally consisting of bronze, and the control face is arranged running exactly between points. The use of such projecting control axle with possibly large diameter for stiffening reasons and corresponding length creates simultaneously the possibility to arrange the so-called snifting valve, required for feeding of working fluid into the inner circulation of the drive, in particularly advantageous manner axially within the control axle, and even to provide still further control devices, as, for instance, a filling pressure-limiting valve or a discoupling valve, likewise in the control axle.

With these and other objects in view which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawings, in which:

FIG. I is a longitudinal section of an axial-piston-unit useable as a pump or a motor, in accordance with the present invention:

H6. 2 is a longitudinal section of a hydrostatic drive consisting of an axial-piston-pump and an axial-piston-motor; and

FIG. 3 is a schematic showing of the distribution of the forces encountered in the unit.

Referring now to the drawings, and in particular to FIG. 1, the axial-piston-unit, useable as a pump or a motor, comprises the following main parts:

The unit comprises a pot-shaped housing 1, the open side of which is closed by a cover 2. In a center bore 3 of the cover 2, a bearing pin 4 is rigidly pressed in, on which a piston drum 5 is adjustably guided by means of two ball or roller bearings 6 and 7, and disposed at opposite ends of the bearing pin 4, spaced apart from each other, so that the resultant force on the barrel is reduced to a minimum, against tipping movements and ir radial direction play free, however adjustable in axial direction. The piston drum 5 contains a plurality of cylindrical bores 8 extending in axial direction, in which bores 8 pistons 9 are sealingly guided. The pistons 9 support themselves under the pressure of the working fluid in the cylinder 8 with their calotte-shaped bottoms 10 on the running ring 11 of a pressure axial bearing 11, 12 and 13, disposed at an angle a in the housing 1. The piston drum 5 is in rotary connection with a shaft 16 projecting from the housing 1 and supported by a ball bearing by means of a gearing 14 movable axially and in limited manner angularly. A pressure spring 17 maintains the end face of the piston drum 5, which end face is formed as a sealing face 18, in case of lacking pressure of the working fluid under an exactly defined face pressure, in engagement with the inner side of the cover 2 which is designed as control disc 19 for the liquid-entrance and -exit to and from, respectively, the cylinders 8. The control disc 19 has for this purpose two kidney-shaped control grooves 20 and 21, respectively, which are in communication by means of bores 22 and 23, respectively, with the connections of the suction and pressure conduits 24 and 25, respectively, and by means of bores 26 in the cylinder drum 5 with the cylinders 8.

Referring now again to the drawings, and in particular to FIG. 2, the hydrostatic drive disclosed therein comprises substantially two equally designed axial-piston-units in accordance with the embodiment disclosed by example in FIG. 1, The units are disposed coaxially on opposite sides of a common control disc 102. As far as the structural elements of this drive coincide with the above described example, they are identified with corresponding end numbers for the pump 100 and for the motor 200. The main distinctions over the axialpiston-unit disclosed in FIG. I reside in the arrangement according to which the pressure bearings 111, 112, 113 and 211, 212, 213 are disposed on swinging bodies 131 and 231, respectively, which can be set at different angles about axes 133 and 233, respectively, which are perpendicular to the rotating axis 132 of the piston drum 105 and 205, respectively, by means of swinging levers 134 and 234, respectively, for a stepless variation of the transmission ratio and of the direction of rotation between the input shaft 116 and the output shaft 216. The bearing pins 104 and 204, respectively, for the two ball and roller bearings 106, 107 and 206, 207, respectively, of j the piston drums 105 and 205, respectively, of the pump side and the motor side are formed in this case by means ofa single control axle 130 pressed into the common control disc 102. The diameter of the control axle 130 is dimensioned so large for obtaining a possibly highest stiffness, that different control devices can be incorporated therein.

In the embodiment disclosed in FIG. 2, these control devices comprise so-called snifting valves 135, one of which is shown only, which valve 135 serve the start of feeding of working fluid from a filling pump (not shown) through a conduit 136 into the control channels 124 and 125, respectively, operating as suction conduits and a discoupling valve 137 for the automatic short circuiting of the control channels 124 and 125 of the suction-and pressure-side dependent upon the filling pressure (for instance during standstill of the drive). Finally, channels 138 and 139 are provided in the control axle 130 for the feeding of a part of after-fed working fluid as lubricating means to the pressure bearings 111, 112, 113 and 211, 212, 213, respectively.

In FIGS. 1 and 3 the position of the resulting load P effective on the piston drum from the supporting forces, attacking on the individual pistons 9, between the calotteshaped ends 10 of the pistons and the rotating ring 11, 111 or 211 of the bearing 12, 112 or 212, is disclosed in an elevational view and in a plan view. Due to the pistons 9 arranged parallel to the rotary axis of the piston drums 5, 105 or 205, for a simpler working of the cylinder bores 8 in the piston drums 5, 105 or 205, the force P exerted on the piston drum in the section planetFlG. 1) extends through the axis of symmetry of the piston drum and can be divided into an axial force component P A and a cross force-component P Due to I the strongly different fluid pressures in the working cylinders of the piston drum 5 on the suction side and the pressure side, the resulting force P on the piston drum with the piston 9 FlG. is disposed, however, outside of the axis of symmetry of the piston drum for the eccentricity e in the view set off for 90 relative to the view shown in H6. 1. The strongly eccentric position of the resultant force on the piston drum 5 brings about a corresponding assymetrically distributed engagement pressure in the control face (shown in dotted lines), in case of a mounting of the piston drum which is yielding angularly to a certain extent. By the mounting of the piston drum 5, stiff against tipping as much as possible and with only slight play, in accordance with the present invention, by means of two needleor roller-bearings 6 and 7, 106 and 107, and 206 and 207, respectively, on a bearing pin 4 which is stiff against bending, as much as possible, it has been achieved to vary the face pressure in the sealing and control face 18 to an at least approximately constant value (shown in full lines). By this manner of mounting, the tipping moment P X e (the piston drum operating resultant force couple); which is effective on the piston drum 5, is balanced out by a couple or supporting moment P X l exerted by the two bearings. The reduction of the largest local face pressure at the edge of the sealing face 18 brought about an extremely high increase of the operating periods in the devices of the present invention to a multiple value without overhauling by refinishing the sealing faces.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

I claim: 1. An axial-piston-unit useable as liquid-pump and as -motor, respectively, comprising:

an outer housing; a control disc mounted to said outer housing and having a control face; 7 a piston drum disposed in and rotable relative to said housing adjacent said control face of said control disc; said piston drum having a plurality of cylinders arranged at equal distance from and parallel to the center axis of said piston drum; a plurality of pistons, each received and sealingly guided in each of said cylinders; a drive-and holding-shaft for said piston drum, an oblique disc disposed in said housing freely directly en gaging abuttingly said pistons such that upon a relative rotation between said piston drum and said oblique disc, each of said pistons performs a reciprocating movement in each of said cylinders, respectively; said control disc having control slots disposed therein facing said piston drum for alternate connection of said cylinders with a suctionand pressure-conduit, respectively; said piston drum including an end face facing said control face of said control disc and having bores communicating with said face; face and connecting said cylinders through said end face of said piston drum into said conduits; said control disc having at least one bearing pin rigidly connected with said control disc and disposed perpendicularly to said control face; needle or roller bearings both mounted operatively substantially free of radial play and located substantially on and at opposite ends of said bearing pin at the greatest distance from each other and constituting a first bearing adjacent said control disc and a second bearing remote from said control disc; said piston drum being guided in radial direction and strongly stiff against tipping during operation, on both of said needle or roller bearings, and said adjacent bearing contributes to the formation of a couple which acts against a piston drum operating resultant force couple acting on the control disc so that the local surface pressure between the piston drum and said control disc is reduced to a minimum, said piston drum however being adjustable in an axial direction about said bearing pin; said piston drum being connected with said driveand holding'shaft for joint rotation and comprising drive means for rotatably driving said piston drum, a direct driving engagement of said drive means with said piston drum being LII 3. The axial-piston-unit, as set forth in claim 1, wherein:

said piston drum is disposed on each of the opposite sides of said control disc and operating as a pump and as a motor, respectively; and

said cylinders of said piston drum being in communication by means of channels connecting kidney-shaped control slots of both control faces and projecting through said control disc. 

